#include <stdio.h>
#include <math.h>

int main(void) {
    int n;
    double sum, term, x;
    scanf("%lf", &x);
    sum = 0;
    term = x;
    for (n = 1; fabs(term) >= 1e-5; n++) {
        sum = sum + term;
        term = term * x * x / (2 * n * (2 * n + 1));
    }
    printf("%.6lf", sum);
    return 0;
}
